Import gettext-0.18.3.
Merge branch 'vendor/gettext' into gettext-0.18.3
MinGW compilation fix for Gettext.

The fix is hacky, something better should be submitted upstream.
Ignore a new autoconf-generated file.
Sync osx-gettext and win-gettext file exclusions.
Don't needlessly build gettext examples & tests.
Don't pass build directory as --prefix.

It may (and typically does) end up in the binary.  Instead, use a
combination of / as the prefix and DESTDIR.
Speed up gettext builds a bit by removing deps tracking.

We clear the whole output directory when building gettext anyway.
Less verbose gettext build.

Use --enable-silent-rules to reduce the noise.
Build gettext with shared libraries on OS X.

Restore building the tools with shared libraries for common code to
reduce the size.  This requires setting up runtime linker paths
correctly.
Don't build gettext manpages and docs either.

This further speeds up the build, as well as making it less fragile on Windows.
Show gettext messages as localized.

Install and ship gettext catalogs too.  Add some hacks to make this
easier to achieve:

- use environment variable POEDIT_LOCALEDIR to override catalogs lookup path
- use POEDIT_USE_UTF8 env. variable to force gettext tools to always output in
   UTF-8 regardless of what they think the console's charset is
Merge Expat into deps/ from vendor/expat.
Build Expat and use it in Gettext on Windows.

Expat is needed to parse Glade XML files in xgettext.  On OS X, we use
system-provided version, but this wasn't the case on Windows.

Fixes #502.
Fix typo in ant libiconv dependencies list.
Use system-provided libexpat on OS X.
Fix bad icon size in the attention bar on Windows.
Merge branch 'gettext-improvements'